1. Field of the Invention
The invention relates to cutting inserts that are installed in a tool holder and intended to be thrown away after becoming dull, in particular, remanufacturing "throw away" inserts so that the remanufactured inserts can be used again.
2. Description of the Related Art
The use of cutting tools having replaceable cutting inserts began as long ago as 1917, when Fred P. Lovejoy invented the use of replaceable blades in order to obtain the economic advantages of having to replace only the dull portion of the tool, not the entire tool itself.
The next major improvement was the invention of the tungsten titanium carbide insert by Philip M. McKenna in 1938, especially for use in milling machines. A typical milling machine is an apparatus that features a rotating mill head having a number of indexable cutting inserts, where the rotating head is passed over the workpiece to remove material (chips) from the workpiece. A "chip" refers to the material that is removed during the cutting process. Ideally, the chips produced should be broken into pieces as small as possible since large chips can interfere with the cutting operation and are dangerous to workers.
Since the time of the invention of the carbide cutting insert, tremendous efforts have been made to understand the myriad factors effecting the performance of cutting inserts. These factors include insert geometry, insert construction, cutting temperature, cutting forces, workpiece material characteristics, and, particularly, chip control.
Kennametal, Inc., founded by inventor Philip McKenna, lists thousands of insert geometries/size/composition/coating combinations and permutations in order to meet the requirements of differing applications.
Inserts can be manufactured in various ways. The most common basic materials are tungsten carbide or tungsten titanium carbide combined with a metallic binder such as cobalt. It is also possible to construct inserts from ceramic material. These are referred to as Cermet. Various thin film coatings can be applied to the surface of the cutting insert. Examples of common thin film coatings are titanium nitride, aluminum oxide, chromium nitride, titanium carbo-nitride, titanium aluminum nitride and diamond. Coatings are used to improve the performance and durability of the insert. Each material/coating combination has a particular application to which it is most suited.
In addition to material choices, various basic geometric shapes can also be selected. The most common are the square, triangle, diamond rhomboid, rectangle, hexagon and round. Added to this complexity is a choice of fifteen different clamping options, five different cutting edge forms, dimension tolerance classification, insert thicknesses, etc.
Some inserts have only one sharpened edge suitable for cutting, however, most indexable inserts have a plurality of cutting edges. Once a particular cutting edge has become dull, the insert is indexed in its holder to expose a new cutting edge. Once all cutting edges are dull, the insert is believed to be useless and is thrown away.
All of the above are incorporated into a standardized insert identification system which enables a customer to accurately order any one of more than a million possible combinations and permutations to meet a particular need. Despite the overwhelming number of insert variations that are available, standard inserts still are "standardized". A new insert's shape, type, size and coating are designed to serve many applications.
In spite of the development of sophisticated technology and vast improvements in the durability and cutting efficiency of cutting inserts and the cost increases commensurate with such advances, cutting inserts are still defined and treated as "throw-away", even in the USA Standard Indexable Inserts for Cutting Tools (B94.25-1969).
An example of efforts to improve the cutting efficiency of inserts is found in U.S. Pat. No. 5,372,463, issued to Takahashi et al. on Dec. 13, 1994. In this patent entitled Throw Away (emphasis added) Insert, it is disclosed that the use of an arcuate small protrusion on the bisector of the nose of the cutting surface will improve chip breaking capabilities of the insert.
U.S. Pat. No. 5,405,711, issued to Noggle on Apr. 11, 1995, is representative of the effort being made to find better materials to construct the insert. Noggle discloses the use of polycrystalline composites to encase the cutting edges of carbide inserts. The polycrystalline material may be diamond, boron nitride or other similar materials. This particular design is said to make the entire insert indexable since the polycrystalline material is presented as a cutting edge around the periphery of the insert.
Still another approach to the improvement of the geometry of the insert is disclosed in U.S. Pat. No. 5,388,932, issued to DeRoche et al. on Feb. 14, 1995. This design is said to provide an efficient positive rake angle when the insert is secured in the milling cutter body.
Pantzar et al. disclose in U.S. Pat. No. 5,421,679, issued on Jun. 6, 1995, the use of a grinding operation intended to be used only along an area against a locating surface of a machine tool. Pantzar et al. disclose that inserts requiring a very high degree of dimensional accuracy have been met by after-grinding the surface(s) adjacent to the cutting edge after the insert is sintered. However, it is said that this grinding (called contour grinding) causes adverse modifications in the micro-geometry of the insert. This invention discloses modification of tool attachment surfaces for improving fit within the tool and avoiding the cutting surfaces.
As disclosed by Pantzar et al., it has been a commonly held truism in the art for more than 45 years that inserts cannot be sharpened once dull without damaging the geometry of the insert. Consequently, this is the reason for the mistaken belief that the inserts must be thrown away once dull.
This belief has been reinforced by failed efforts to regrind used inserts to gain additional useful life before the insert must be discarded. The most ambitious of the regrinding attempts to reclaim dulled inserts, frequently referred to as "down-sizing", is provided by North American Carbide, Inc. of Broken Arrow, Okla. In this process, the "scrap"/used insert is reground using specially adapted grinding machinery so that an insert that is virtually identical to the original, only slightly smaller is obtained. Unfortunately, the success of this process has been rather limited. Since the reground insert is smaller than the original, the reground insert does not fit accurately in the original tool holder. Since the reground insert is smaller overall, the inscribed circle is also reduced. Inscribed circle is defined as the largest internal circle that can be drawn such that all sides of the insert are tangent to that circle. This can sometimes be countered by the use of shims, however, the use of shims then complicates the installation process. Many companies initially embraced this concept, recognizing the significant financial advantage of being able to increase the life span of an insert. However, the difficulties sometimes encountered with clamping the inserts to fit accurately in the tool holder once it had been refurbished quickly diminished the enthusiasm for the approach. Consequently, the belief that cutting inserts are only capable of a one time use and then must be thrown away continues to prevail after all these years.
A method of grinding a cutting insert, either using a new insert or a dulled insert, that will provide sharpened edges with cutting performance equal to or exceeding a new insert and that will provide an insert which can be held in a tool holder without the use of shims or special holders is not known in the prior art.